ptonsparky
Tom
- Occupation
- EC - retired
How many of you series two 240 volt control relay coils to make use of the 480 being supplied to the unit?
Customer supplied roto phase.
Customer supplied roto phase.
Panel builders
- Thread starter ptonsparky
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I wouldn't trust the coils to be similar enough to divide the voltage equally.
ptonsparky
Tom
- Occupation
- EC - retired
It is what they did.
kwired
Electron manager
- Location
- NE Nebraska
I don't see them being that much different that they won't still be within a reasonable tolerance. HVAC guys parallel control transformers when "twinning" units sometimes, I think there is more risk of unequal division issues with something like that.
ptonsparky
Tom
- Occupation
- EC - retired
One relay is not being used other than for the VD.
Not something I was expecting to see on a listed piece of equipment. I haven’t found that little sticker yet either.
Not something I was expecting to see on a listed piece of equipment. I haven’t found that little sticker yet either.
kwired
Electron manager
- Location
- NE Nebraska
Kind of is a hack, and shouldn't be original design, but does work in a pinch when servicing, usually with intent to come back and replace with the right item.
ptonsparky
Tom
- Occupation
- EC - retired
Brand new out of the box yesterday.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
A UL inspector would not likely allow it, you are using the relays in a way not intended per their listing.
ptonsparky
Tom
- Occupation
- EC - retired
I don't see any labeling or listing marks.
That said it 'purrs like a pussycat' as my dad would have said.
That said it 'purrs like a pussycat' as my dad would have said.
MidwestJest141
Member
- Location
- Midwest
- Occupation
- Electrical Engineer - Power and Controls
In this scenario what stops the current from choosing one relay over the other? I see a potential imbalance of load on one of the relays. In the case of this imbalance you might burn out one of the relays... This issue comes about because of the possible difference in coil resistance...this can not be guaranteed to match perfectly from relay to relay even of the same p#. Just my 2 cents, Thanks!
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
210730-1145 EDT
If these were relays with a DC coil I doubt there would be any problem. Coil resistances, and currents at a voltage are likely quite close.
Generally relays have a pull in voltage considerably below their nominal operating voltage, possibly 70%, and dropout is lower. Probably a greater ratio for a DC than an AC relay.
In an AC relay you have both coil resistance and inductance to look at. Coil resistance will be quite close and it is not affected by armature position. Armature position has a great effect on inductance, and therefore impedance dependent upon no excitation, and fully powered. I might expect to see much greater variation in the steady state impedance when energized than what I see in resistance.
Dynamically when the relays are closing the impedance vs time comparison between the two relays may be the greatest variable. An AC relay coil impedance greatly increases as the relay is energized.
One would certainly need to run tests on series AC relays to see how they perform on both the transient turn on and steady state conditions, and over a range of lower voltages.
The problem, if one exists, could be corrected by putting an appropriate capacitor, or resistor in parallel with each relay coil. The other way is to parallel the two coils, if two relays are really needed, and use a step-down transformer for power.
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If these were relays with a DC coil I doubt there would be any problem. Coil resistances, and currents at a voltage are likely quite close.
Generally relays have a pull in voltage considerably below their nominal operating voltage, possibly 70%, and dropout is lower. Probably a greater ratio for a DC than an AC relay.
In an AC relay you have both coil resistance and inductance to look at. Coil resistance will be quite close and it is not affected by armature position. Armature position has a great effect on inductance, and therefore impedance dependent upon no excitation, and fully powered. I might expect to see much greater variation in the steady state impedance when energized than what I see in resistance.
Dynamically when the relays are closing the impedance vs time comparison between the two relays may be the greatest variable. An AC relay coil impedance greatly increases as the relay is energized.
One would certainly need to run tests on series AC relays to see how they perform on both the transient turn on and steady state conditions, and over a range of lower voltages.
The problem, if one exists, could be corrected by putting an appropriate capacitor, or resistor in parallel with each relay coil. The other way is to parallel the two coils, if two relays are really needed, and use a step-down transformer for power.
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
If you are talking about a UL508a inspector, I suspect they would not even notice unless it was their quarterly point of emphasis item.
kwired
Electron manager
- Location
- NE Nebraska
If they are in series, current is always going to be the same through both coils. Voltage drop across each individual coil can vary if impedances are not the same though.
Input voltage of 492, with variances you could have 239 across one but that means the remaining 253 has to drop across the other, but if they are the same model I wouldn't expect them to even be that far off from one another.
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